Prohibit DROP EXTENSION bdr when BDR is active

Closes #206

Author: ringerc

bdr_commandfilter.c

@@ -714,6 +714,42 @@ bdr_commandfilter_dbname(const char *dbname)
 	}
 }
 
+static void
+prevent_drop_extension_bdr(DropStmt *stmt)
+{
+	ListCell   *cell;
+
+	/* Only interested in DROP EXTENSION */
+	if (stmt->removeType != OBJECT_EXTENSION)
+		return;
+
+	/* Check to see if the BDR extension is being dropped */
+	foreach(cell, stmt->objects)
+	{
+		ObjectAddress address;
+		List	   *objname = lfirst(cell);
+		Relation	relation = NULL;
+
+		/* Get an ObjectAddress for the object. */
+		address = get_object_address(stmt->removeType,
+									 objname, NULL,
+									 &relation,
+									 AccessExclusiveLock,
+									 stmt->missing_ok);
+
+		if (!OidIsValid(address.objectId))
+			continue;
+
+		/* for an extension the object name is unqualified */
+		Assert(list_length(objname) == 1);
+
+		if (strcmp(strVal(linitial(objname)), "bdr") == 0)
+			ereport(ERROR,
+					(errmsg("Dropping the BDR extension is prohibited while BDR is active"),
+					 errhint("Part this node with bdr.part_by_node_names(...) first, or if appropriate use bdr.remove_bdr_from_local_node(...)")));
+	}
+}
+
 static void
 bdr_commandfilter(Node *parsetree,
 				  const char *queryString,
@@ -858,6 +894,8 @@ bdr_commandfilter(Node *parsetree,
 			{
 				DropStmt   *stmt = (DropStmt *) parsetree;
 
+				prevent_drop_extension_bdr(stmt);
+
 				if (EventTriggerSupportsObjectType(stmt->removeType))
 					break;
 				else

expected/part_bdr.out

@@ -4,6 +4,10 @@
 CREATE SCHEMA "some $SCHEMA";
 CREATE TABLE "some $SCHEMA"."table table table" ("a column" integer);
 CREATE SEQUENCE "some $SCHEMA"."some ""sequence"" name" USING bdr;
+-- Dropping the BDR extension isn't allowed while BDR is active
+DROP EXTENSION bdr;
+ERROR:  Dropping the BDR extension is prohibited while BDR is active
+HINT:  Part this node with bdr.part_by_node_names(...) first, or if appropriate use bdr.remove_bdr_from_local_node(...)
 -- Initial state
 SELECT node_name, node_status FROM bdr.bdr_nodes ORDER BY node_name;
     node_name    | node_status 
@@ -129,6 +133,11 @@ WARNING:  Node node-pg is in state k not expected 'r'. Attempting to remove anyw
 
 (1 row)
 
+-- BDR is parted, but not fully removed, so don't allow the extension
+-- to be dropped yet.
+DROP EXTENSION bdr;
+ERROR:  Dropping the BDR extension is prohibited while BDR is active
+HINT:  Part this node with bdr.part_by_node_names(...) first, or if appropriate use bdr.remove_bdr_from_local_node(...)
 -- Strip BDR from this node entirely and convert global sequences to local.
 SELECT bdr.remove_bdr_from_local_node(true, true);
 WARNING:  forcing deletion of possibly active BDR node

sql/part_bdr.sql

@@ -7,6 +7,9 @@ CREATE SCHEMA "some $SCHEMA";
 CREATE TABLE "some $SCHEMA"."table table table" ("a column" integer);
 CREATE SEQUENCE "some $SCHEMA"."some ""sequence"" name" USING bdr;
 
+-- Dropping the BDR extension isn't allowed while BDR is active
+DROP EXTENSION bdr;
+
 -- Initial state
 SELECT node_name, node_status FROM bdr.bdr_nodes ORDER BY node_name;
 
@@ -90,6 +93,10 @@ SELECT node_name, node_status FROM bdr.bdr_nodes ORDER BY node_name;
 -- so a warning will be generated.
 SELECT bdr.bdr_part_by_node_names(ARRAY['node-pg']);
 
+-- BDR is parted, but not fully removed, so don't allow the extension
+-- to be dropped yet.
+DROP EXTENSION bdr;
+
 -- Strip BDR from this node entirely and convert global sequences to local.
 SELECT bdr.remove_bdr_from_local_node(true, true);